This invention relates to a fused solid electrolytic capacitor, and more particulary to a fusing arrangement of a chip type solid electrolytic capacitor.
Chip type solid electrolytic capacitors are used widely in various electronic circuits. It has a fault rate which is small. The fault thereof, if it occurs, is often in a mode of a short circuit. When the short circuit happens, a large short-circuit current flows to heat the capacitor element and sometimes to burn the capacitor element. For protecting other circuit components from this excessive short-circuit current, a fuse is incorporated into a solid electrolytic capacitor. As for prior art, there is such a solid electrolytic capacitor with a fuse incorporated therein as disclosed in U.S. Pat. No. 4,107,762 issued on Aug. 15, 1978.
The fusing arrangement in this prior art has a fundamental structure wherein one end of an external cathode lead is fixed by an adhesive insulating resin to a cathode layer on a side surface of a capacitor element. The resin adhesive insulates the cathode lead from the cathode layer of the capacitor element. One end of a fuse wire is connected to one end of a cathode lead, and the other end of the fuse wire is connected to the cathode layer on the side surface of the capacitor element. In such a fusing arrangement, there is the possibility that, in a process for fixing the external cathode lead against this adhesive resin layer and hardening the adhesive resin, a part of the cathode lead may pierce through the adhesive resin layer to make contact with the cathode layer.
To avoid such a possibility of a short-circuit, the thickness of the adhesive resin layer should be made large enough, e.g., 1 mm or more. However, conponents used in a chip type solid electrolytic capacitor must be very small in size in order to provide for miniaturization. For instance, the thickness of external leads is about 0.5 mm and the diameter of a fuse element is about 50 .mu.m to 100 .mu.m. Therefore, the adhesive resin layer having a thickness of 1 mm or more is an obstacle to prevent further reduction of the total size of the fused solid electrolytic capacitor.
Another shortcoming of fusing arrangements in the cited prior art is that the effective length of the fuse element is not constant, because the intermediate portion of the fuse wire may tend to make contact with the cathode layer on the side surface and its contacting portion varies. Furthermore, owing to the above reason, it is difficult to make the effective length of the fuse element long enough.